Inkjet recording head and inkjet recording apparatus having the same

ABSTRACT

An inkjet recording head includes a passage communicating with a discharge port for discharging ink, a discharging heater provided in the passage for generating energy to discharge ink from the discharge port, and a detecting unit provided in the passage for detecting a temperature of ink that changes in accordance with heat energy generated by the detecting unit and a flow of ink in the passage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to inkjet recording apparatuses, and moreparticularly, to an inkjet recording apparatus that can detect defectivedischarging. Herein, the term “recording” includes applications of ink(printing) to ink support materials such as cloth, strings, paper, andsheet materials. The term “recording apparatus” includes variousinformation apparatuses and printers serving as output devices of theapparatuses.

2. Description of the Related Art

Along with the popularization of information processing apparatuses suchas copying machines, word processors, and computers, recordingapparatuses (inkjet recording apparatuses) that perform recording withan inkjet recording head have been rapidly popularized as output(recording) apparatuses for the information processing apparatuses.

In general, an inkjet recording apparatus includes a carriage on which arecording head and an ink tank are mounted, a conveying mechanism forconveying a recording medium, and a control circuit for controlling thecarriage and the conveying mechanism.

When an ink discharging operation is not performed by the recording headfor a long period, the viscosity of ink in an ink passage near adischarge port increases, and the ink is sometimes not dischargednormally. Further, if a minute bubble, which grows in the ink in the inkpassage for discharging, remains in the ink passage, normal inkdischarging is sometimes difficult. This phenomenon of defectivedischarging due to the remaining bubble pronouncedly appears when theprint duty is relatively high. In another case, a bubble enters the inkat a connecting portion of an ink supply passage or an ink supplysystem, and clogs the ink supply passage. This sometimes hinders normaldischarging.

If recording failure is caused by the above-described defective inkdischarging, the recording medium is wasted, and the time taken forrecording is also wasted. If unclear images are continuously recorded ina so-called “faded recording” state caused immediately before defectivedischarging occurs, multiple recording media are wasted. Further, ifrecording is continued in the “faded recording” state, the recordinghead is heavily loaded, and this sometimes destroys the recording headitself.

In order to avoid the above-described trouble, variousdefective-discharging detecting devices have been proposed. A typicaldefective-discharging detecting device is an opticaldefective-discharging detecting device including a light-emittingportion and a light-receiving portion for receiving light from thelight-emitting portion. In this optical defective-discharging detectingdevice, light from the light-emitting portion is blocked by ink dropletsdischarged from discharge ports. On the basis of the change in output ofthe light-receiving portion (change in amount of received light),defective discharging is detected.

Japanese Patent Laid-Open No. 2-194967 discloses an inkjet recordingapparatus including an optical defective-discharging detecting device.

FIGS. 16A and 16B explain an operation of detecting defectivedischarging of ink. FIG. 16A is a schematic view showing a state inwhich ink discharged from a recording head passes through an opticalpath between a light-emitting portion and a light-receiving portion, andFIG. 16B is a waveform chart showing an output waveform from thelight-receiving portion in this case. FIGS. 17A and 17B also explain anoperation of detecting defective discharging of ink. FIG. 17A is aschematic view showing a state in which ink discharging is abnormal, andFIG. 17B is a waveform chart showing an output waveform from thelight-receiving portion in this case.

Referring to these figures, a recording head 1 includes a plurality ofink discharge ports 2. Electrothermal transducers (heaters) 3 areprovided in the corresponding passages (nozzles) communicating with theink discharge ports 2. When a discharging pulse (rectangular pulse) forcausing ink discharging is applied to an electrothermal transducer 3,ink in the corresponding passage is heated by heat energy from theelectrothermal transducer 3. An ink droplet 2005 is thereby dischargedfrom the corresponding ink discharge port 2.

As shown in FIG. 16A, the ink droplet 2005 discharged from an inkdischarge port 2 passes through the optical path of light emitted from alight-emitting portion 2001 toward a light-receiving portion 2002. Whenpassing through the optical path, the ink droplet 2005 blocks light fromthe light-emitting portion 2001, and the amount of light received by thelight-receiving portion 2002 is thereby decreased. In this case, thelevel of an output signal 2006A from the light-receiving portion 2002 islower than a threshold value 2004, as shown in FIG. 16B.

In contrast, when an ink droplet 2005 is not discharged from an inkdischarge port 2, as shown in FIG. 17A, or when an ink droplet 2005discharged from an ink discharge port 2 is too small, the amount oflight received by the light-receiving portion 2002 does not changesignificantly. In this case, the level of an output signal 2006B fromthe light-receiving portion 2002 is higher than the threshold value2004, as shown in FIG. 17B.

When the level of the output signal from the light-receiving portion2002 is lower than or equal to the threshold value 2004 (the state shownin FIG. 16B), it is determined that the ink discharging operation isnormal. In contrast, when the level of the output signal from thelight-receiving portion 2002 is higher than the threshold value 2004(the state shown in FIG. 16B), it is determined that the ink dischargingoperation is abnormal (defective discharging).

When it is determined that the ink discharging operation is abnormal, acarriage motor is controlled so as to move a carriage, on which therecording head 1 is mounted, to a position where a suction cap isprovided. Then, a suction-cap motor is controlled so as to cap the inkdischarge ports 2 of the recording head 1 with the suction cap, and inkis sucked from the recording head 1 by a suction pump. As necessary, thecarriage motor is controlled so as to move the recording head 1 to aposition where a cleaning plate is provided, and the ink discharge ports2 are cleaned with the cleaning plate.

After ink suction, it is judged again whether the ink dischargingoperation is normal or abnormal. When it is determined again that theink discharging operation is abnormal, a message indicating “abnormal”is displayed on a display (for example, an LCD) in the recordingapparatus so as to urge the user to refill ink or to replace therecording head. When it is determined that the ink discharging operationis normal, recording is started.

A recording head disclosed in Japanese Patent Laid-Open No. 58-118267 isa liquid discharging device in which a plurality of nozzles arearranged, and in which conductors for detecting the change intemperature are provided in passages (nozzles) between the adjacentelectrothermal transducers (beside the electrothermal transducers).Unfortunately, the above-described inkjet recording apparatus has thefollowing problems.

A plurality of ink droplets are simultaneously discharged from aplurality of discharge ports, and the change in output from thelight-receiving portion caused when the ink droplets block the opticalpath is detected. Therefore, it is difficult to make judgment aboutdefective discharging of ink with respect to each discharge port. It isconceivable to detect the change in output from the light-receivingportion by discharging an ink droplet from only one discharge port. Inthis case, however, the change in output from the light-receivingportion caused when one ink droplet blocks the optical path is small,and therefore, it is difficult to make an accurate judgment aboutdefective discharging of ink. Further, the optical defective-dischargingdetecting device is susceptible to external light, which also makesdetection of defective discharging difficult. In this way, it isdifficult to make an accurate judgment about defective discharging withrespect to each discharge port.

Moreover, a defective-discharging detecting operation cannot beperformed during recording on a recording medium. For this reason, theuser needs to perform a defective-discharging detecting operation beforerecording on the recording medium in order to check whether inkdischarging failure has occurred in the inkjet recording head. Thisdefective-discharging detecting operation decreases the throughput ofthe recording apparatus.

SUMMARY OF THE INVENTION

The present invention provides an inkjet recording head that overcomesthe above-described problems and that can accurately detect inkdischarging failure with a high throughput, and an inkjet recordingapparatus using the inkjet recording head.

An inkjet recording head according to an embodiment of the presentinvention includes a passage communicating with a discharge port fordischarging ink, an energy generating element, provided in the passage,for generating energy to discharge ink from the discharge port, and adetecting unit, provided in the passage, for detecting a temperature ofink that changes in accordance with heat energy generated by thedetecting unit and a flow of ink in the passage.

An inkjet recording apparatus according to another embodiment of thepresent invention includes the above-described inkjet recording head;and a control unit configured to control driving of the inkjet recordinghead.

According to the present invention, an ink flow caused in the passagewhen discharging ink (ink flow caused by ink refilling) is detected.When discharging failure occurs, the flow of ink is smaller than duringnormal discharging. By utilizing this difference in magnitude of the inkflow, judgment can be made about ink discharging failure.

The magnitude of the ink flow in the case of discharging failure has asufficiently distinguishable difference from that during normaldischarging. Therefore, it is possible to accurately distinguish betweennormal discharging and defective discharging.

Further, the detection accuracy will not be reduced by externalinfluence, unlike the optical defective-discharging detecting device.This allows for highly accurate detection.

Since the ink flow can be detected for each discharge port, judgmentabout discharging failure of the recording head can be made for eachdischarge port.

Still further, since judgment about discharging failure can be performedduring normal ink discharging operation, the throughput of the recordingapparatus is higher than that of a recording apparatus including anoptical defective-discharging detecting device.

According to the present invention, the detecting unit generates heatenergy in response to generation of energy by the energy generatingelement, and the temperature of the ink is then detected. Therefore, itis possible to further increase the accuracy in detecting inkdischarging failure.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a part of a substrate in an inkjetrecording head according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the substrate, taken along lineII-II in FIG. 1.

FIG. 3 is a plan view showing another structure of a flow sensor used inthe inkjet recording head of the first embodiment.

FIGS. 4A and 4B explain the principle of operation of the flow sensor inthe inkjet recording head of the first embodiment. FIG. 4A is acharacteristic view showing how the output voltage changes when an inkflow is formed, and FIG. 4B is a characteristic view showing how theoutput voltage changes when there is no ink flow.

FIG. 5 is a block diagram of a driving circuit in an ink-flow detectorused in the inkjet recording head of the first embodiment.

FIGS. 6A to 6E explain the principle of operation of the ink-flowdetector shown in FIG. 5.

FIGS. 7A and 7B explain the behavior of ink in a passage displayed whendischarging is performed in the inkjet recording head of the firstembodiment. FIG. 7A is a schematic view showing the behavior of ink inthe passage during normal discharging, and FIG. 7B is a schematic viewshowing the behavior of ink in the passage displayed when a dischargeport is covered with extra ink and defective discharging is causedthereby.

FIG. 8 is a flowchart showing a defective-discharging detectingprocedure performed in the inkjet recording head of the firstembodiment.

FIGS. 9A to 9E explain the principle of operation of a flow sensor in aninkjet recording apparatus according to a second embodiment of thepresent invention.

FIG. 10 is a partial sectional view of an inkjet recording headaccording to a third embodiment of the present invention.

FIG. 11 is a partial sectional view of an inkjet recording headaccording to a fourth embodiment of the present invention.

FIGS. 12A to 12E explain the principle of operation of a detectingelement used in the inkjet recording head of the fourth embodiment.

FIG. 13 is a partial sectional view of an inkjet recording headaccording to a fifth embodiment of the present invention.

FIG. 14 is a schematic view showing structures of a recording head andits surroundings in an inkjet recording apparatus to which the presentinvention can be applied.

FIG. 15 is a schematic view of a surface of the recording head shown inFIG. 14 on which ink discharge ports are provided.

FIGS. 16A and 16B explain a defective-discharging detecting operationperformed in an inkjet recording head.

FIG. 16A is a schematic view showing a state in which ink dischargedfrom a recording head passes through the optical path between alight-emitting portion and a light-receiving portion, and FIG. 16B is awaveform chart showing an output waveform from the light-receivingportion.

FIGS. 17A and 17B explain a defective-discharging detecting operationperformed in the inkjet recording head.

FIG. 17A is a schematic view showing a state ink discharging isabnormal, and FIG. 17B is a waveform chart showing an output waveformfrom the light-receiving portion.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will now be described withreference to the drawings.

FIG. 14 is a schematic view showing structures of a recording head andits surroundings in an inkjet recording apparatus to which the presentinvention can be applied. Referring to FIG. 14, the inkjet recordingapparatus is a serial inkjet color printer. The inkjet recordingapparatus includes a recording head 1 having a plurality of lines ofnozzles, and a carriage on which the recording head 1 is mounted. Bydischarging ink droplets from the recording head 1, an image is recordedon a recording medium 12.

FIG. 15 is a schematic view of a surface of the recording head 1 onwhich ink discharge ports 2 are provided. The ink discharge ports 2 arearranged in two lines and in a zigzag formation in the main scanningdirection.

Although not shown in FIG. 14, the inkjet recording apparatus includes acontrol unit that controls the driving of the recording head 1. As therecording head 1, a recording head according to, but not limited by, anyof the following first to fifth embodiments can be used. The controlunit controls the operation of the entire inkjet recording apparatus,and also performs a recovery operation when ink discharging failureoccurs in the recording head 1.

Recording heads according to embodiments of the present invention willbe described below.

First Embodiment

FIG. 1 is a schematic view showing a part of a substrate in an inkjetrecording head according to a first embodiment of the present invention.FIG. 2 is a cross-sectional view of the substrate, taken along lineII-II in FIG. 1.

Referring to FIG. 1, a heater board 10 has a structure in which a commonliquid chamber 18 is provided at the center thereof, as viewed in adirection perpendicular to the board surface. On each side of the commonliquid chamber 18 in the heater board 10, a heater unit 3A including aplurality of discharging heaters 3 arranged in line is provided.

Dummy resistors (not shown) are provided near the heater units 3A. Thedummy resistors are not used for discharging of ink droplets. Thedischarging heaters 3 are electrothermal transducers (discharging-energygenerating elements) that generate heat energy in accordance with theapplied voltage, and are connected to terminals 4 to which a drivingsignal is applied. The terminals 4 are connected to external terminals(output terminals of a driving-signal supply circuit) by wire bonding.When a driving signal is applied to a terminal 4, the correspondingdischarging heater 3 is driven.

The discharging heater 3 is provided in each passage communicating witha discharge port. Each passage communicates with the common liquidchamber 18, and incorporates a flow sensor 5 serving as a detectingelement for detecting the change in ink flow in the passage.

As shown in FIG. 2, the discharging heater 3 and the flow sensor 5 canbe provided on the same substrate surface. The flow sensor 5 can beformed as a film-shaped sensor by the same film deposition process asthat for the discharging heater 3.

A protective film 6 serving as an insulating film is provided on thesurface where the discharging heater 3 and the flow sensor 5 areprovided, and a cavitation-resistant film 7 is provided on theprotective film 6. By coupling the heater board 10 (first member) havingthe cavitation-resistant film 7 to a nozzle forming member 20 (secondmember), a passage 18 a serving as a nozzle communicating with adischarge port 2 is formed. The passage 18 a is provided on thecavitation-resistant film 7, and communicates with the common liquidchamber 18.

The discharging heater 3 is provided in a portion of the member thatdefines the passage 18 a (heater board 10) facing the discharge port 2.When the discharging heater 3 is driven, heat energy generated by thedischarging heater 3 is applied to ink in the passage 18 a, and a bubbleis thereby generated in the ink in the passage 18 a. By the pressure ofgrowth of the bubble, the ink is discharged from the passage 18 athrough the discharge port 2. This method for discharging ink bygenerating a bubble is generally called a bubble jet method.

After growing by heat energy, the bubble contracts. Thecavitation-resistant film 7 prevents an impact caused by contraction ofthe bubble from being transmitted to the discharging heater 3 and theprotective film 6. The cavitation-resistant film 7 is formed of a metalhaving a high melting point, for example, tantalum.

The flow sensor 5 is provided in a portion of the heater board 10between the discharge port 2 and an ink supply port through which ink issupplied into the passage 18 a. The flow sensor 5 detects the flow ofink in the passage 18 a. Similar to other portions, the flow sensor 5can be formed with high precision by a semiconductor film depositionprocess.

The flow sensor 5 is formed of a material whose resistance varies inaccordance with the temperature. Specifically, the flow sensor 5 can beformed of, for example, aluminum, titanium, and tantalum that form theother components, or platinum, tantalum nitride, and titanium nitridethat are frequently used as temperature-measuring resistors. Among thesematerials, aluminum can be used as an electrode. Tantalum can beprovided at the top of the sensor in order to improve the resistance tocavitation. The line width of the sensor may be increased in order toreduce variations in wiring resistance in a process of forming the flowsensor. Further, in order to output a high voltage in response to even aslight temperature change, a wiring pattern of the sensor may have ameander shape that increases the resistance of the sensor.

While the flow sensor 5 is provided in the heater board 10 in the firstembodiment, it may be provided at any position that allows detection ofthe ink flow in the passage 18 a communicating with the discharge port2. For example, as shown in FIG. 3, a flow sensor 14 may be provided ina bridge portion formed by anisotropic edging so as to be spatiallyinsulated from the heater board 10. A pair of holes 13 are provided inthe heater board 10 so as to oppose each other across the flow sensor14. The holes 13 are connected in the heater board 10 so that aconnecting portion therebetween passes under the bridge portion wherethe flow sensor 14 is provided.

The principle of operation of the flow sensor 5 will now be described.

FIGS. 4A and 4B explain the principle of operation of the flow sensor 5.FIG. 4A is a characteristic view showing how the output voltage changeswhen there is an ink flow, and FIG. 4B is a characteristic view showinghow the output voltage changes when there is no ink flow.

In FIG. 4A, a characteristic A1, shown by a one-dot chain line,indicates the change in output voltage of the flow sensor 5 made whenthe ink flow rate is 10 l/h, and a characteristic A2, shown by a solidline, indicates the change in output voltage of the flow sensor 5 madewhen the ink flow rate is 20 l/h. These characteristics A1 and A2 areobtained on the basis of the change in temperature (flow ratecharacteristic) of ink in the passage. The change in temperature ismeasured by the following procedure.

The temperature of ink in the common liquid chamber 18 is set at 25° C.When a current is supplied to the flow sensor 5, the flow sensor 5generates heat, and ink in the passage 18 a is heated by the energy ofheat. After a first pulse current having a pulse width of a size thatdoes not generate a bubble in the ink is passed through the flow sensor5 to heat the ink in the passage 18 a, the ink in the common liquidchamber 18 is made to flow in the direction of arrow Q in FIG. 2. Then,a second pulse current having a pulse width smaller than the pulse widthof the first pulse current is passed through the flow sensor 5, and thechange in temperature of ink on the flow sensor 5 in the passage 18 a isdetected. The second pulse current has an intensity of such a size thatink on the flow sensor 5 in the passage 18 a is not heated by heatenergy generated from the flow sensor 5 by the second pulse current.

The first pulse current and the second pulse current are passed throughthe flow sensor 5 in order, and the resistance of the flow sensor 5 ismeasured. In this case, since the temperature of the flow sensor 5 israrely increased by the measuring currents, the output voltage of theflow sensor 5 varies in accordance with the temperature of ink near theflow sensor 5. When the ink flow rate is high, much ink having atemperature lower than that of the heated ink flows into the passage 18a, and therefore, the temperature of ink near the flow sensor 5decreases. When the ink flow rate is low, the amount of exchanged heatis smaller than when the flow rate of refilled ink is high, andtherefore, the temperature of ink near the flow sensor 5 does notdecrease easily. In other words, the characteristics A1 and A2 indicatethat it becomes easier to decrease the temperature and the amount ofchange in the resistance per unit time increases as the flow rateincreases.

In contrast, when ink does not flow on the flow sensor 5, a first pulsecurrent is passed through the flow sensor 5 to heat ink near the flowsensor 5, a second short pulse current is passed through, and theresistance of the flow sensor 5 is then measured. As a result,characteristics shown in FIG. 4B are obtained. In FIG. 4B, acharacteristic B1, shown by a solid line, a characteristic B2, shown bya one-dot chain line, and a characteristic B3, shown by a broken lineindicate temperature characteristics of the flow sensor 5 when the inkflow rate is zero. The characteristics B1, B2, and B3 respectivelycorrespond to cases in which the temperatures of ink serving as fluidare 25° C., 35° C., and 45° C. As shown by the characteristics B1, B2,and B3, the resistance of the flow sensor 5 increases as the temperatureof ink before the first pulse current is applied thereto increases, andthe output voltage of the flow sensor 5 also increases in accordancewith the ink temperature.

As described above, the surroundings (that is, ink) of the flow sensor 5are heated by passing a first pulse current through the flow sensor 5.Then, a second pulse current having a pulse width smaller than the pulsewidth of the first pulse current is passed through the flow sensor 5,and a change in the temperature of the ink on the flow sensor 5 inaccordance with the ink flow rate is detected. On the basis of thecharacteristic curves shown in FIGS. 4A and 4B, the change in the inkflow rate can be found from the output voltage (resistance) obtainedwhen the second pulse current is applied.

FIG. 5 shows a driving circuit of an ink-flow detector used in theinkjet recording head according to the embodiment of the presentinvention.

The driving circuit shown in FIG. 5 includes a detecting circuit fordetecting an ink flow with a detecting element 17, and a control circuitfor controlling the driving of an electrothermal transducer 15 andcontrolling a detecting operation of the detecting circuit in connectionwith the driving of the electrothermal transducer 15. The electrothermaltransducer 15 corresponds to the discharging heater 3 shown in FIGS. 1and 2. The detecting element 17 corresponds to the flow sensor 5 servinga heat-generating and temperature-measuring resistor shown in FIGS. 1and 2, or the flow sensor 14 serving as a heat-generating andtemperature-measuring resistor shown in FIG. 3. The control circuit isprovided in each discharging nozzle (discharge port).

The detecting circuit is a constant-current driving circuit, andincludes a constant-current source 16, a detecting element 17, and a MOStransistor 11. The constant-current source 16 and the detecting element17 are connected in series via the MOS transistor 11. One end of thedetecting element 17 is connected to one terminal of theconstant-current source 16 and to a line of a voltage VSS via the MOStransistor 11. The other end of the detecting element 17 is connected tothe other terminal of the constant-current source 16. A comparatorcircuit 37 is connected to a line that connects the other end of thedetecting element 17 and the other terminal of the constant-currentsource 16.

One end of the electrothermal transducer 15 is connected to a groundline GNDH via a MOS transistor 38. The other end of the electrothermaltransducer 15 is connected to a voltage supply line VH. The controlcircuit includes two AND circuits 36 a and 36 b. The AND circuit 36 areceives a heater application signal HE, a block selection signal BLE,and recording data DATA, and ANDs these received data. The AND circuit36 b receives a block selection signal BLE, print data DATA, and a biassignal BIAS, and ANDs these received data. The output of the AND circuit36 a is supplied as a switch-element control signal to the MOStransistor 38 via an amplification circuit 39. The output of the ANDcircuit 36 b is supplied as a switch-element control signal to the MOStransistor 11.

In the control circuit, a one-bit selection period is designated by ablock selection signal BLE. Since recording data DATA is set at a highlevel (corresponding to “1”) in the one-bit selection period, the outputof the AND circuit 36 a is high while the block selection signal BLE ishigh. During the period when the output of the AND circuit 36 a is high,the MOS transistor 38 is turned on so as to supply a voltage to theelectrothermal transducer 15.

A switch-element control signal output from the AND circuit 36 b is highwhile a bias signal BIAS is high. During the period when theswitch-element control signal is high, the MOS transistor 11 is turnedon. When the MOS transistor 11 is on, a current is supplied from theconstant-current source 16 to the detecting element 17.

In the detection circuit, the current is supplied to the detectingelement 17 in synchronization with the flow of ink due to heat energyfrom the electrothermal transducer 15, and the change in ink flow isdetected as a temperature change.

Specifically, an output voltage V_(out) is detected at both ends of thedetecting element 17 in the detection circuit. The MOS transistor 11functions as a switch element. The MOS transistor 11 is turned on insynchronization with the ink flow so as to heat ink on the detectingelement 17, and is then turned off. In synchronization with apredetermined timing while the ink is flowing or after the ink flow iscompleted, the MOS transistor 11 is turned on again, and the temperatureof the ink on the detecting element 17 is measured. In this case,switching is made between a state in which the detecting element 17functions as a heat-generating resistor and a state in which thedetecting element 17 functions as a temperature-measuring resistor, bychanging the pulse driving time of the detecting element 17.

While only one detecting circuit is adopted in the driving circuit shownin FIG. 5, normally, a plurality of detecting circuits are connected inparallel. One control circuit is provided for each detection circuit. Inthis case, detection signals from the detecting circuits (voltagesV_(out) output from both ends of the detection elements 17) are outputin a time-sharing manner by performing control so that the MOStransistors 11 are sequentially turned on.

FIGS. 6A to 6E explain the principle of operation of the ink-flowdetector shown in FIG. 5. FIG. 6A is a waveform chart of the voltageapplied to the electrothermal transducer 15. FIG. 6B shows the change inink flow rate on the time axis when the direction from the common liquidchamber 18 to the discharge port 2 shown in FIG. 1 is a positivedirection. FIG. 6C is a waveform chart of the current applied to thedetecting element 17. FIG. 6D shows the change in temperature on thetime axis of ink on the detecting element 17. FIG. 6E is a waveformchart of the detected output voltage in accordance with the changes inink flow rate and ink temperature shown in FIGS. 6B and 6D.

As shown in FIG. 6C, a pulse current supplied to the detecting element17 includes a pulse that has a long pulse width P1 and is high during aperiod between a time t₀ and a time t₁, and a pulse that has a shortpulse width P2 (<P1) and that is high during a period between a time t₂and a time t₃. The pulse having the pulse width P1 and the pulse havingthe pulse width P2 are supplied at a predetermined interval. The periodbetween the time t₀ and the time t₁ where the pulse current having thepulse width P1 is applied is a heating period for heating ink near thedetecting element 17. The period between the time t₂ and the time t₃when the pulse current having the pulse width P2 is applied is adetection time for detecting an ink flow by measuring the temperature ofink near the detecting element 17.

By supplying the driving pulse current shown in FIG. 6A to theelectrothermal transducer 15, heat is generated by the electrothermaltransducer 15, and a bubble is formed in the ink in the passagecommunicating with the ink discharge port. Consequently, an ink dropletis discharged from the ink discharge port.

FIGS. 7A and 7B are schematic views explaining the behavior of inkexhibited in the passage during a discharging operation of the recordinghead in the first embodiment. FIG. 7A shows the behavior of ink in thepassage during normal discharging, and FIG. 7B shows the behavior of inkin the passage in the case of defective discharging caused by coveringthe discharge port with extra ink.

First, the behavior of ink during normal discharging will be describedwith reference to FIG. 7A.

When a voltage is applied to the electrothermal transducer 15(discharging heater 3) shown in FIG. 5, a boiling phenomenon occurs in apart of the ink in contact with the cavitation-resistant film 7 in thepassage, so that a bubble grows. With this growth of the bubble, aninterface of the ink bulges toward the front side of the discharge port2, and a bubble region spreads over an area from the vicinity of thedischarge port 2 to the back inner portion of the passage (see a timet_(B) in FIG. 7A).

When the application of the pulse is completed, the formed bubbledissipates. In response to this dissipation, the bulging front part ofink separates, travels through the air, and then lands on a recordingmedium. Further, the remaining part of the bulging ink is drawn backinto the passage by a negative pressure generated by dissipation (see atime t_(C) in FIG. 7A).

When ink is refilled in the state at the time t_(C) in FIG. 7A, the inkinterface moves toward the vicinity of the discharge port 2. This inkflow is caused by a capillary force near the leading end of the passage.As a result, when a bubble is formed, as shown in FIG. 6B, the inktemporarily flows to the common liquid chamber 18, and then flows fromthe common liquid chamber 18 to the discharge port 2 after the volume ofthe bubble increases to its maximum.

When ink refilling is completed, a normal state at a time t_(E) shown inFIG. 7A is brought about again. Every time a voltage is applied to theelectrothermal transducer 15 (discharging heater 3), the operations fromthe time t_(A) to the time t_(E) shown in FIG. 7A are repeated.

The behavior of ink in the case of defective discharging will now bedescribed with reference to FIG. 7B. At a time t_(A) in FIG. 7B, thedischarge port 2 is covered with extra ink. In this case, when a voltageis applied to the electrothermal transducer 15 (discharging heater 3), abubble grows because of a boiling phenomenon, but ink separation doesnot occur (see a time t_(B) and a time t_(C) in FIG. 7B). Since ink isnot discharged by the growth of the bubble in this way, the amount ofink that is reduced by an ink discharging operation is zero. For thisreason, the amount of ink to be refilled is smaller and the timenecessary for ink refilling is shorter than when normal discharging isperformed.

When ink near the flow sensor 5 is heated in synchronization with theflow of ink in the above-described normal discharging and defectivedischarging operations, the temperature of the ink changes in accordancewith the ink flow rate, as shown in FIG. 6D. While the ink flow rate ishigh during normal discharging, it is low during defective discharging.When the flow rate of the ink flowing from the common liquid chamber 18toward the discharge port 2 is high, the temperature of the ink on theflow sensor 5 decreases significantly. In contrast, when the flow rateof the ink flowing from the common liquid chamber 18 toward thedischarge port 2 is low, the decrease in the temperature of the ink onthe flow sensor 5 is smaller than when the ink flow rate is high.

The voltage output from the flow sensor 5 differs in accordance with theink flow rate. In FIG. 6E, a solid line shows a voltage output from theflow sensor 5 during normal discharging, and a broken line shows anoutput from the flow sensor 5 during defective discharging. During theperiod from the time t₂ to the time t₃, the voltage output from the flowsensor 5 differs between normal discharging and defective discharging.Therefore, by comparing the voltages V_(out) output from both ends ofthe detecting element 17 with a threshold value V_(out,th) for judgmentabout defective discharging in the period from the time t₂ to the timet₃, it can be judged whether defective discharging has occurred in therecording head.

A description will be given below of conditions for distinguishingbetween normal discharging and defective discharging in the recordinghead.

(1) Normal Discharging:

(output voltage V_(out))≦(threshold value V_(out,th))

(2) Defective Discharging:

(output voltage V_(out))>(threshold value V_(out,th))

Herein, it is preferable that the threshold value V_(out,th) besufficiently large so as to avoid misjudgment due to a noise signal andbe sufficiently small so as to allow judgment immediately after theoccurrence of defective discharging.

The output voltage V_(out) and the threshold value V_(out,th) arecompared by the comparator circuit 37 shown in FIG. 5. The result of thecomparison performed by the comparator circuit 37 is supplied to thecontrol unit that controls the recording head. Using the comparisonresult, when the output voltage V_(out) is more than the threshold valueV_(out,th), the control unit determines that ink discharging failure hasoccurred, and carries out a predetermined operation. The predeterminedoperation includes, for example, a discharging recovery operation ofoperating the recording head for discharging recovery, an operation ofprotecting the recording head, and an operation of giving the user awarning.

While the threshold value V_(out,th) for judgment about defectivedischarging is a fixed value in the first embodiment, it may be given bya high-dimensional function using the temperature in the passage as avariable. Alternatively, a data table listing optimum threshold valuesV_(out,th) set for the respective ink temperatures may be prepared sothat an appropriate threshold value can be selected therefrom inaccordance with the temperature of ink in the passage. The optimumthreshold values V_(out,th) are set by the control unit.

While the heat characteristic of the discharging heater is fixed in thefirst embodiment, a data table listing threshold values ranked inaccordance with variations in the heat characteristic of the dischargingheater may be prepared so that an appropriate threshold value can beselected therefrom in accordance with the rank. The appropriatethreshold value is selected by the control unit.

By thus setting the optimum threshold values V_(out,th) in the datatable, accurate judgment about defective discharging can be made,regardless of the temperature in the passage.

FIG. 8 is a flowchart showing a defective-discharging detectingprocedure according to the first embodiment. Defective discharging isdetected by using a data table listing optimum threshold valuesV_(out,th).

First, the temperature of ink in the passage is detected with the flowsensor 5 (Step S10). For temperature detection, a data table showing therelationship between the temperature and the output voltage (orresistance) when a constant current is passed through the flow sensor 5is created beforehand. With reference to the data table, the temperatureis obtained from the output voltage of the flow sensor 5.

Next, with reference to a data table listing optimum threshold valuesV_(out,th) set corresponding to the ink temperatures, an optimumthreshold value (threshold value V_(out,th)) corresponding to thedetected ink temperature is selected (Step S11).

Then, a predetermined voltage is applied to the discharging heater 3(Step S12). Heat energy is thereby applied to the ink in the passage,and a bubble is generated. By growth and contraction of the bubble(bubble generation and dissipation), ink discharging and refilling areperformed (Step S13).

In conjunction with the ink flow due to bubble generation anddissipation, a first pulse current is supplied to the flow sensor 5(Step S14). Then, a second pulse current is supplied to the flow sensor5, an output voltage V_(out) in this case is detected (Step S15), andthe ink heating operation with the flow sensor 5 is completed (StepS16).

Subsequently, the output voltage V_(out) obtained in Step S15 and thethreshold value V_(out,th) selected in Step S11 are compared (Step S17).When the output voltage V_(out) is more than the threshold valueV_(out,th), it is determined that ink discharging failure has occurred(Step S18). When the output voltage V_(out) is less than or equal to thethreshold value V_(out,th), it is determined that ink discharging isnormal (Step S19).

In the recording head according to the first embodiment, the flow of inkin the passage produced when ink is discharged (ink flow produced byrefilling) is detected. The ink flow is smaller when discharging failureoccurs than when discharging is normal. By utilizing the difference inmagnitude of ink flow, discharging failure of ink can be detected.

Since the magnitude of ink flow in the case of discharging failure has asufficiently distinguishable difference from that in normal discharging,it is possible to accurately distinguish between the normal dischargingstate and the defective discharging state.

Since the detection accuracy is not reduced by an external influence,unlike the optical defective-discharging detecting unit, accuratedetection is possible.

Since the ink flow can be detected at each discharge port, judgmentabout defective discharging can be made for each discharge port in therecording head.

Since judgment about defective discharging can be made during the normaldischarging operation, the throughput of the recording apparatus ishigher than that of a recording apparatus having an opticaldefective-discharging detecting unit.

While judgment about defective ink discharging is made during printingin the first embodiment, it may be made between successive printingoperations on printing media. Alternatively, defective discharging maybe automatically detected after a predetermined time.

Second Embodiment

An inkjet recording head according to a second embodiment has a basicconfiguration similar to that of the recording head of the firstembodiment except in an operation of detecting defective dischargingwith a flow sensor. The inkjet recording head of the second embodimentalso includes an ink-flow detector (ink-flow detecting unit) similar tothat shown in FIG. 5.

FIGS. 9A to 9E explain the principle of operation of the ink-flowdetector. FIG. 9A is a waveform chart of the voltage applied to theelectrothermal transducer 15. FIG. 9B shows the change in ink flow rateon the time axis when the direction from the common liquid chamber 18 tothe discharge port 2 shown in FIG. 1 is a positive direction. FIG. 9C isa waveform chart of the current applied to the detecting element 17.FIG. 9D shows the change in temperature on the time axis of ink on thedetecting element 17. FIG. 9E is a waveform chart of the detected outputvoltage in accordance with the changes in ink flow rate and inktemperature shown in FIGS. 9B and 9D.

As shown in FIG. 9C, a pulse current supplied to the detecting element17 includes a pulse that has a short pulse width P3 and that is highduring a period between a time t₄ and a time t₅, and a pulse that has along pulse width P4 (>P3) and that is high during a period between atime t₆ and a time t₇. The pulse having the pulse width P3 and the pulsehaving the pulse width P4 are supplied at a predetermined interval. Theperiod between the time t₄ and the time t₅ where the pulse currenthaving the pulse width P3 is applied is a detecting period for measuringthe temperature of ink near the detecting element 17. The period betweenthe time t₆ and the time t₇ when the pulse current having the pulsewidth P4 is applied is a detection time for detecting the ink flow bymeasuring the change in resistance of the detecting element 17 whileheating the ink near the detecting element 17.

As shown in FIG. 9B, the ink flow rate differs between normaldischarging and defective discharging. When ink near the detectingelement 17 is heated in synchronization with the ink flow, thetemperature of the ink on the detecting element 17 changes, as shown inFIG. 9D. In FIG. 9D, a solid line shows the change in temperature madewhen the ink flow rate is high, and a dotted line shows the change intemperature made when the ink flow rate is low.

When the ink flow rate is high, the amount of increase in temperature ofthe ink on the detecting element 17 is small. In contrast, when the inkflow rate is low, the ink on the detecting element 17 stays for a longtime without flowing, and therefore, is continuously heated by thedetecting element 17. As a result, the amount of increase in the inktemperature is larger than when the ink flow rate is high. Therefore, asshown in FIG. 9E, the output voltage from the detecting element 17differs when the flow rate is high (solid line) and when the flow rateis low (dotted line) during the period from the time t₆ to the time t₇.

By comparing the output voltage V_(out) at both ends of the detectingelement 17 (flow sensor) and the threshold value V_(out,th), judgment ismade about defective discharging of the recording head. The conditionsfor distinguishing between normal discharging and defective dischargingare similar to those adopted in the first embodiment. The thresholdvalue V_(out) for judgment about defective discharging may be changed inaccordance with the temperature of ink in the passage measured duringthe period from the time t₄ to the time t₅.

The recording head according to the second embodiment providesadvantages similar to those of the recording head of the firstembodiment.

Third Embodiment

FIG. 10 is a partial sectional view of an inkjet recording headaccording to a third embodiment of the present invention. In thisrecording head, a nozzle forming member 20 that defines a passage bybeing combined with a heater board (head substrate) is not formed of anorganic material, but of silicon (Si). In this nozzle forming member 20,a flow sensor 5 serving as an ink flow-rate detecting element is formedby a film deposition process similar to the process for a semiconductor.Other structures are similar to those adopted in the first embodiment.

The flow sensor 5 may have a meandering shape in order to increase theresistance, or may have a square shape.

The inkjet recording head of the third embodiment also includes anink-flow detector having a configuration similar to that shown in FIG.5. The ink-flow detector operates in a manner similar to that adopted inthe first embodiment.

Since the flow sensor 5 is provided apart from a discharging heater 3 inthe third embodiment, it is not susceptible to heat generated by bubblegeneration. Therefore, it is possible to more accurately detect the inkflow.

Fourth Embodiment

FIG. 11 is a partial sectional view of an inkjet recording headaccording to a fourth embodiment of the present invention. The inkjetrecording head of the fourth embodiment has a configuration similar tothat adopted in the first embodiment except in the structure of adetecting element.

The detecting element includes flow sensors 21 and 23 (first and secondresistors) and a heater 22 (heating element). The flow sensor 21, theheater 22, and the flow sensor 23 are provided between a dischargingheater 3 for generating a bubble in ink and a common liquid chamber 18in a region below a passage 18 a. The flow sensors 21 and 23 arearranged symmetrically with respect to the heater 22.

When ink flows in the direction of arrow Q in FIG. 11, the flow sensor23 is provided upstream from the ink flow, and the flow sensor 21 isprovided downstream from the ink flow. The heater 22 is interposedbetween the flow sensors 21 and 23.

The operation of the flow sensors 21 and 23 in the fourth embodimentwill now be described.

In a case in which the heater 22 is controlled at a temperature higherthan the ambient temperature, a temperature distribution in thedirection of arrow Q is symmetrical with respect to the heater 22 whenthere is no ink flow. When ink in the passage 18 a moves in thedirection of arrow Q, ink is supplied from the common liquid chamber 18onto the upstream flow sensor 23. By this ink supply, an upper portionof the flow sensor 23 is cooled. On the other hand, heat conduction fromthe heater 22 to an upper portion of the downstream flow sensor 21 ispromoted by the ink flow, and therefore, the temperature of the upperportion of the flow sensor 21 increases. As a result, a temperaturedifference is formed between the flow sensors 21 and 23. By convertingthe temperature difference into a voltage, an output voltage inaccordance with the flow rate is obtained. On the basis of the outputvoltage, the ink flow rate can be detected.

FIGS. 12A to 12E explain the principle of operation of the detectingelement. FIG. 12A is a waveform chart of the voltage applied to thedischarging heater 3. FIG. 12B shows the change in ink flow rate on thetime axis when the direction from the common liquid chamber 18 to thedischarge port 2 is a positive direction. FIG. 12C is a waveform chartof the current applied to the heater 22. FIG. 12D is a waveform chart ofthe current applied to the flow sensors 21 and 23. FIG. 12E shows adetected output voltage on the time axis obtained by subtracting theoutput voltage of the flow sensor 23 from the output voltage of the flowsensor 21.

As shown in FIG. 12B, the ink flow rate in normal discharging isdifferent from that in defective discharging during a period between atime t₁₃ and a time t₁₄. During a period from a time t₁₂ to the timet₁₄, the heater 22 is controlled at a high temperature that does notgenerate a bubble in the ink in synchronization with ink refilling, anda temperature difference between the flow sensors 21 and 23 is measuredduring the period. A detected output voltage V_(out) is calculated froma voltage difference formed by the temperature difference between theflow sensors 21 and 23. By comparing the detected output voltage V_(out)with a threshold value V_(out,th), judgment is made about defectivedischarging. The conditions for distinguishing between normaldischarging and defective discharging are similar to those adopted inthe first embodiment.

As described above, defective discharging can be detected, regardless ofthe temperature in the passage.

In the fourth embodiment, the two flow sensors 21 and 23 are arrangedsymmetrically with respect to the heater 22. This allows more accurateand more stable detection of the flow rate.

The recording head of the fourth embodiment also provides advantagessimilar to those of the recording head of the first embodiment.

Fifth Embodiment

FIG. 13 is a partial sectional view of an inkjet recording headaccording to a fifth embodiment of the present invention.

The inkjet recording head of the fifth embodiment is a piezo recordinghead, and includes a nozzle plate 28 having a plurality of dischargeports 24, a vibrating plate 29 having piezoelectric elements providedcorresponding to the discharge ports 24, and a liquid-chamber capacitycontrol portion 25 for controlling the vibrating plate 29. Thepiezoelectric elements are discharging-energy generating elements thatgenerate energy for discharging ink from the discharge ports 24, and canadjust the capacity of a liquid chamber communicating with the dischargeports 24.

The nozzle plate 28 is provided with a base 27 including flow sensors 26serving as detecting elements. By coupling the nozzle plate 28 havingthe base 27 to a substrate having the vibrating plate 29, a plurality ofpassages are formed. Each passage communicates with the liquid chamber.By applying a driving signal corresponding to recording information tothe liquid-chamber capacity control portion 25, ink is discharged fromthe discharge ports 24. The flow sensors 26 are formed as film-shapedsensors by the same film deposition process as that for the base 27.

In addition to the above-described structure, the inkjet recording headof the fifth embodiment also includes a defective-discharging detectingunit (not shown) that detects defective ink discharging of the dischargeports 24 with the flow sensors 26 provided corresponding to thedischarge ports 24. The defective-discharging detecting unit detects theflow of ink by measuring the change in resistance of the flow sensor 26while heating ink near the flow sensor 26 by the application of avoltage.

In the inkjet recording head of the fifth embodiment, a large amount ofink is refilled in response to the amount of discharged ink in the caseof normal discharging. In contrast, in the case of defectivedischarging, the ink flow is smaller than in normal discharging.Therefore, ink near the flow sensor 26 is not heated easily.Accordingly, judgment can be made about defective discharging of therecording head by detecting the temperature difference of ink near theflow sensor due to the difference in ink flow rate between normaldischarging and defective discharging and comparing the voltagecorresponding to the detected temperature difference with a thresholdvalue for judgment about defective discharging. This judgment isperformed in a procedure similar to that adopted in the firstembodiment.

The recording head of the fifth embodiment also provides advantagessimilar to those of the recording head of the first embodiment.

While the present invention is applied to the recording head used in aserial printer in the above-described embodiments, it is not limitedthereto. The present invention is also applicable to a so-calledfull-multi type recording head used in a line printer in which dischargeports are arranged in line over the entire width of a recording medium.In particular, since this recording head is long because multipledischarging heaters are arranged, the present invention can beeffectively and easily applied thereto.

The configurations of the above-described embodiments can be combinedappropriately. For example, the detecting element (flow sensor 21,heater 22, and flow sensor 23) used in the fourth embodiment can beapplied to the detecting elements in the other embodiments.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications and equivalent structures and functions.

This application claims the benefit of Japanese Application No.2007-254449 filed Sep. 28, 2007, which is hereby incorporated byreference herein in its entirety.

1. An inkjet recording head comprising: a passage communicating with adischarge port for discharging ink; an energy generating element,provided in said passage, for generating energy to discharge ink fromthe discharge port; and a detecting unit, provided in said passage, fordetecting a temperature of ink that changes in accordance with heatenergy generated by said detecting unit and a flow of ink in saidpassage.
 2. The inkjet recording head according to claim 1, wherein saidenergy generating element is provided in a portion of said passagefacing the discharge port.
 3. The inkjet recording head according toclaim 1, wherein said passage is formed by coupling a heater board,having a protective insulating film and a cavitation-resistant film, toa nozzle forming member.
 4. The inkjet recording head according to claim3, wherein said detecting unit is provided at a portion of the heaterboard between the discharge port and an ink supply port through whichthe ink is supplied into said passage.
 5. The inkjet recording headaccording to claim 3, wherein said detecting unit is provided in thenozzle forming member.
 6. The inkjet recording head according to claim5, wherein the nozzle forming member is formed of silicon.
 7. The inkjetrecording head according to claim 1, wherein the heat energy generatedby said detecting unit does not generate a bubble in the ink.
 8. Theinkjet recording head according to claim 1, wherein said detecting unitdetects a voltage corresponding to a resistance that changes inaccordance with temperature.
 9. The inkjet recording head according toclaim 1, wherein said detecting unit comprises a heating elementconfigured to generate the heat energy, and first and second resistorsarranged symmetrically with respect to said heating element, the firstand second resistors having resistances that change in according withthe temperature.
 10. The inkjet recording head according to claim 9,wherein the heating element generates the heat energy and is used todetect a voltage corresponding to a difference between the resistancesof the first and second resistors.
 11. An inkjet recording apparatuscomprising: an inkjet recording head comprising a passage communicatingwith a discharge port for discharging ink, an energy generating element,provided in the passage, for generating energy to discharge ink from thedischarge port, and a detecting unit, provided in the passage, fordetecting a temperature of ink that changes in accordance with heatenergy generated by the detecting unit and a flow of ink in the passage;and a control unit configured to control driving of said inkjetrecording head.
 12. The inkjet recording apparatus according to claim11, wherein the detecting unit detects a voltage corresponding to aresistance that changes in accordance with temperature, and wherein saidcontrol unit judges a discharging state of ink from the discharge porton the basis of the detected voltage.
 13. The inkjet recording apparatusaccording to claim 11, wherein said inkjet recording head comprises aplurality of passages and discharge ports, with an energy generatingelement and a detecting unit provided in each of the passages.
 14. Amethod for detecting defective discharging of an inkjet recording head,comprising the steps of: discharging ink by supplying a driving pulse toan energy generating element to generate a bubble in ink in a passagecommunicating with an ink discharge port; applying at least one pulse toa flow sensor; measuring an output voltage from the flow sensor; andcomparing the output voltage from the flow sensor with a threshold valueto determine a level of ink flow in the passage.
 15. The method fordetecting defective discharging of an inkjet recording head according toclaim 14, wherein two pulses are applied to the flow sensor when adriving pulse is applied to the energy generating element.